Exemplary embodiments of the present invention relate to a method for preforming a textile semi-finished product having the steps (a) arranging a textile, and wherein the textile comprises (i) at least two layers of fibers that are at least in part arranged on top of each other, and/or (ii) interwoven fibers and/or fiber bundles, on a substrate; (b) fixing-in-position of the fibers of the textile against each other; and (c) thereafter cutting-to-size of the textile, and wherein the fixing-in-position of the fibers of the textile comprises an irradiation step with a laser beam so that a melt-on binder of the textile is melted on in a localized fashion only and not evaporated.
According to a second aspect, exemplary embodiments of the present invention relates to a preforming apparatus for preforming a textile semi-finished product.
Preforming is a step in the manufacture of building components made of fibrous composite materials. After the cutting-to-size step, the cutting edges of the textile are normally no longer fixed in position. This causes the textile to become frayed easily; a dropped stitch in a seam causing a run can undo the seam holding the fabric together and may result in the textile losing its desired arrangement when it is incorporated as a semi-finished product in the manufactured component.
Therefore, it is known in the art to use a textile that comprises a melt-on binder. Before the textile is cut to size, it is heated in an oven resulting in the fusing of individual fibers of the textile. Subsequently, the textile is cut to size, and because the fibers are agglutinated, any fraying is prevented.
The thus obtained semi-finished product is quite rigid, which renders it difficult to fit it into a corresponding component mold for subsequent impregnation and curing.
German Patent Document DE 199 52 443 A1 discloses a method in which the different layers of the textile are sewn to each other in order to achieve the necessary slip-proofness that is necessary for the cutting process. This technique, however, still results in the textile tending to fray along its seams.
German Patent Document DE 693 04 042 T2 discloses a method and an apparatus for manufacturing structurally reinforced preforms. These preforms are interconnected at individual sites by melting-on a binder. Several layers are fastened to each other in this way, which provides better handling properties. But the method described therein can also lead to fraying.
German Patent Document DE 35 41 954 C2 discloses a method for the manufacture of composite bodies that can be used to produce composite bodies having sharp edges. To this end, the synthetic resin that is present in the textile is partially cured, while the individual fiber layers are separated from one another by thin, elastic separating film. These separating films are removed after the fact and the partially cured fiber layers are pressed into the finished composite body. The specification does not address the problem of fraying during cutting.
U.S. Pat. No. 5,418,035 A discloses a method for manufacturing a composite fiber component in which the individual layers of a textile are first fastened to each other at one edge in order to then insert the textile in the mold. This patent does not address the problem of fraying during cutting.
German Patent Document DE 10 2007 032 904 B3 discloses a method for the structural fixation of a textile two-dimensional construct that seeks to prevent any falling apart of the textile semi-finished product during the cutting-to-size step by simple means. Future load scenarios are simulated to this end, and the locations in the semi-finished product are identified in relation to the resulting finished component that will undergo only minimal displacement due to stresses. The textiles are connected with each other at these locations. The method is not configured to prevent fraying.
Exemplary embodiments of the present invention are directed to preventing frayed edged on textile semi-finished products.
Advantageously, exemplary embodiments of the present invention provide that the fibers of the textile are interconnected adjacent to the later cut-to-size line, meaning the later cut-to-size edge, thereby preventing fraying along the edges. It is also advantageous that this fixing in position will not lead to excessive stability and rigidity in the emerging preform. The resulting preform thus maintains its draping capacity and can also be adjusted to double-curved geometries. Moreover, it is possible to produce preforms that are small and of complex designs.
It is furthermore advantageous that no allowance is necessary along the edges as is required with prior art methods. In a strength calculation such edges cannot be considered as carrying, which leads to elevated component weights in the finished component.
Furthermore, it is advantageous that the fixing-in-position step can be implemented by a laser in an automated fashion. This is possible, in particular, because the laser beam can be guided over the textile without touching it. The area in which the fibers are interconnected is quite narrow so that the resulting preform remains unstable. For example, the laser beam is selected accordingly so that the fibers are interconnected across a width of less than one centimeter.
It is advantageous relative to inductive heating, for example, that the substrate upon which the textile is placed can be freely selected. No metal items may be nearby during inductive heating. If microwave radiation is used, it must be ensured that said radiation does not escape in the environment because this may cause injury to persons in the surrounding area.
Another advantageous aspect of the invention is that using the laser it is possible to achieve an even warm-up. Temperature measurements can be provided, for example, during the irradiation of the textile, such as by touch-less measuring. The laser's power, the diameter of the laser beam and/or the speed by which the laser advances can be adjusted accordingly so that a preset temperature will not be exceeded thus preventing damage to the textile. Moreover, it can be ensured that the temperature will not fall below a preset temperature place value thus guaranteeing secure interconnecting of the fibers inside the textile.
In the context of the present invention the fixing in position of the fibers of the textile is understood to mean that the fibers are interconnected at least locally in order to reduce the incidence of fraying during the subsequent cut-to-size step. It is preferred for the melt-on binder to be already present as part of the textile. But theoretically it would also be possible to apply the binder to the textile immediately before irradiation by the laser beam.
Cutting-apart is generally understood to mean, in particular, a separating action that can be achieved by the use of a mechanical tool; but it does not necessarily have to be a mechanical tool.
The binder is understood to mean, in particular, a melt-on material that is disposed in the vicinity of the fibers of the textile or that itself is present in the form of fibers. The binder can be incorporated in the textile or located on the textile. During the melt-on step the binder interconnects the fibers that are located in the surrounding area.
According to exemplary embodiments of the present invention, the fixing-in-position of at least two layers occurs along a fix-in-position line; while, in contrast, the cutting-to-size action occurs along the cut-to-size line. The fix-in-position line is arranged at a distance from the cut-to-size line that is selected in such a way as to reduce or suppress fraying of the textile altogether. For example, this distance may be between 0 mm and 5 mm. This causes the fraying that starts at the cut-to-size line to come to a halt at the latest when a dropped stitch, which had its origin at the cut-to-size line, reaches the fix-in-position line.
To fix the fibers in position, a preferred embodied example can provide that the layers are covered by a film that is transparent for laser light and the laser beam is irradiated through the film. The characteristic of the film being transparent for the light of the laser is understood to mean, in particular, that absorption and reflection together are less than 20%. By an adequate selection of the films it is possible to achieve transmission rates of above 90%. The higher the transmission rate, the lower are the losses and the fewer precautions must be taken to protect the environment against scattered laser light.
In particular, the film is transparent for laser radiation in such way that it does not melt on itself during the irradiation. Preferably, the film is selected at least in such a way that it comprises sufficiently pronounced separating surface properties, thus allowing the film to be removed again from the layers after the two layers have been fixed in position. Furthermore, preferably, the film is selected in such a way that the laser beam, if incident perpendicularly, is reflected at a maximum of 30% relative to its power.
The characteristic that the laser beam is incident in such a way that the melt-on binder of the textile is only melted on in a localized fashion and not evaporates is understood to mean, in particular, that an irradiation power and advancing speed of the laser are selected in such a way that a damage-causing temperature, which may lead to damage to the binder or the textile, is not exceeded at any location. In particular, the power density of the laser beam is selected in such a way that no significant charring occurs, meaning that there may be a certain amount of thermally induced damage to a portion of the binder and/or the fibers of the textile; however, the damage is so minimal that it does not have to be taken into account for the calculation of the strength of the component that is manufactured from the textile semi-finished product. In particular, the power density of the laser beam is selected in such a way that any thermally induced damage to the textile and/or the binder results only in a loss of strength that is less than 10%.
With regard to the fix-in-position and cut-to-size steps, it is preferred for the method to be automated. It is also conceivable to envision the step of arranging the at least two layers of the textile in an automated step.
According to one preferred embodied example, the textile is arranged on a substrate and air is suctioned out of the area between the substrate and the film prior to irradiation with the laser light. This causes the fibers to be fixed in position relative to each other and relative to the substrate. The lowered pressure furthermore lowers the risk of oxidation during heating. It is also possible to envision that the area between the film and the substrate is purged with an inert gas prior to the irradiation with the laser beam. It is beneficial for the residual pressure to be below 200 mbar, in particular less than 100 mbar.
Preferably, the textile is fixed in position before it is cut to size using a mechanical cutting device. Alternatively, the cutting-to-size action is achieved by a laser; specifically the same laser that is used for the fixing-in-position action. But this option can have the disadvantage that, during the cutting action, there may be thermally induced damage to the fibers and/or the binder resulting in a possible loss of strength of the completed component.
The steps of arranging, cutting-to-size and fixing-in-position can be repeated for several textile layers until a preformed semi-finished product comprising a plurality of textile layers has been manufactured. Moreover, before arranging a further textile layer on the already cut-to-size preform, it is possible to place a film thereon, evacuate the intermediate space, then connect the preform with the additional textile layer using a laser, and afterwards cut the additional textile layer to size. It is possible to implement the fix-in-position action first then cut apart. But it is also possible to implement both steps simultaneously, or cut apart first and then fix in position.
An apparatus that is suitable as a preform apparatus according to the invention for preforming a textile semi-finished product is designed and configured for the manufacture of a plurality of textile semi-finished products. In particular, the substrate, the cut-to-size device and the fix-in-position device are fastened to each other. Moreover, the cut-to-size device and the fix-in-position device are normally automated devices that are operated by a motor.
The substrate is understood to mean any device that is able to fix the layers of the fibers of the textile in position. The substrate can include a table, but an air-impermeable conveyor belt is also possible.
According to one preferred embodied example, the preform apparatus comprises a trigger unit that is designed to move the laser along the fibers of the textile, specifically in such a way that the fibers of the textile are fixed in position along the fix-in-position line; and for moving the cut-to-size device specifically in such a way that it cuts each layer apart along the cut-to-size line respectively, and wherein the fix-in-position line is located at a distance relative to the cut-to-size line that is so small that any fraying of the textile is reduced or suppressed altogether.
For example, the cut-to-size line can be arranged at a distance of less than 10 mm from the fix-in-position line. The trigger unit can be connected with input means and can use said means to establish the position of the cut-to-size line and/or the fix-in-position line in relation to the substrate. The trigger unit can, for example, have an interface that will allow reading in CAD data.
Preferably, the trigger unit is adjusted for moving the laser at a speed that is selected in relation to the intensity of the beam in such a way that the binder is only melted on, but not evaporated or charred, during irradiation with the laser beam. To this end, the trigger unit is connected with a temperature measuring device that measures the temperature at the location where the laser beam is located at a given instance.
The fix-in-position device preferably comprises a film placement device for placing a film and a differential pressure application device for applying a differential pressure causing the film to hug the two-dimensional textile. This film placement device can be automated, for example.
Preferably, the preform apparatus comprises a shielding device that is taken along in such a way that it absorbs any reflected parts of the laser beam. Thus, any hazard to persons in the area is avoided.